MedicalResearch.com Interview with:
Dr. Stephen Burgess PhD
Programme Leader at the Medical Research Council Biostatistics Unit
University of Cambridge
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: Lipoprotein(a) is a lipoprotein subclass, and an important biomarker for coronary heart disease. As a clinical biomarker, it has a similar story to LDL-cholesterol (“bad” cholesterol), in that it is thought to be a causal risk factor for coronary heart disease, and so is a potential target for drug development. However, while drugs that lower LDL-cholesterol, such as statins, have been successful in reducing coronary heart disease risk, drugs that lower lipoprotein(a) have not as yet been successful. New drugs are currently in development that specifically target lipoprotein(a) and can lower lipoprotein(a) concentrations by 80-90%. We performed this study to investigate whether these drugs are likely to be successful in reducing coronary heart disease risk.
We compared individuals with naturally-occurring genetic variants that predispose them to a higher or lower lifetime concentration of lipoprotein(a) as a way of mimicking a randomized controlled trial. This approach has previously been undertaken for other biomarkers, including LDL-cholesterol. We found that having 10mg/dL lower genetically-predicted concentration of lipoprotein(a) was associated with a 5.8% reduction in coronary heart disease risk.
However, associations between genetically-predicted LDL-cholesterol and coronary heart disease risk are quantitatively much stronger than the proportional effect of LDL-cholesterol lowering on coronary heart disease risk as estimated by statin trials. This is because differences in genetic variants reflect lifelong changes in LDL-cholesterol, whereas statin trials only lower LDL-cholesterol for a few years. Hence, using the ratio between the genetic and trial estimates for LDL-cholesterol, we estimate that lowering lipoprotein(a) by 10mg/dL in a short-term clinical trial would only reduce coronary heart disease risk by 2.7%. To obtain the same reduction in coronary heart disease risk of around 20% as observed in statin trials, lipoprotein(a) would have to be lowered by around 100mg/dL. This explains why previous trials of less specific and less potent lipoprotein(a)-lowering drugs have failed to demonstrate benefit.